Power harvesting wireless transmitter

ABSTRACT

Apparatus for a power harvesting wireless transmitter. The wireless transmitter includes a magnet, an inductor, a power supply, a processor, and a transmitter with an antenna. The magnet interacting with the inductor provides a sole source of power sufficient to power the transmitter. The inductor is connected to the power supply. The power supply includes a voltage multiplier, a storage unit, and, in one embodiment, a voltage regulator. The processor includes at least one input connected to one or more local switches, sensors, and instruments. The processor outputs an identifier and data corresponding to the inputs. The processor output is connected to the transmitter, which sends a wireless signal containing the identifier and data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/640,108, filed Apr. 30, 2013, and U.S. Provisional Application No.61/783,202, filed Mar. 14, 2013.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND

This invention pertains to a wireless monitoring system with aself-powered transmitter. More particularly, this invention pertains toa wireless transmitter with a power harvesting circuit supplying powerto a processor and a transmitter.

DESCRIPTION OF THE RELATED ART

Rotating and moving machines are in widespread use for many industrialprocesses. These processes often require local sensors and instrumentsto monitor various parameters with the sensors and instruments wired toremote control and monitoring panels. Traditionally, a sensor orinstrument is mounted on or next to the machine and wiring is needed toprovide power to the sensor and/or to send a signal from the sensor to aremotely mounted monitor. In an automobile, wiring from a sensormeasuring engine speed and/or tire rotational speed adds complexity andcost during manufacturing and maintenance because of the constraintsinherent in a vehicle. In industrial applications, wiring from sensorson rotating, reciprocating, and linear machines adds complexity andcosts because of the environment and distance between such equipment andthe remote monitoring equipment.

Traditional sensors and instruments need a power source, eitherindependent and connected to the device or supplied through the signalcircuit. Independent power supplies from external sources and frombatteries create reliability problems for the instrumentation systembecause the instrumentation power source is typically independent of thepower source for the machine being monitored.

BRIEF SUMMARY

According to one embodiment of the present invention, a power harvestingwireless transmitter system is provided. The power harvestingtransmitter is a wireless monitoring system that has no need forexternal wiring for a power source or for sending the signal from thesensor to a remote location. In this way the wireless transmitter isself-contained with a reliable power source and without external wiringfor power and connectivity.

The power harvesting wireless transmitter system includes a magnet and amulti-sensor transmitter that is responsive to the magnet. The magnet isdimensioned and configured to be attached to a moving component of amachine. The magnet is dimensioned to be have a short interaction timecompared to a dwell time where the magnet does not interact with thetransmitter. The multi-sensor transmitter includes an inductor, a powersupply, a processor, and a transmitter with an antenna. The magnetinteracting with the inductor generates sufficient power to energize theprocessor and transmitter. The magnet interacting with the inductor isthe sole source of power for the wireless transmitter system.

In one embodiment, the magnet moving relative to an inductor coilinduces a current/voltage spike in the inductor. The inductor coil isconnected to a power supply that includes a voltage multiplier, astorage circuit, and a voltage regulating circuit. The voltagemultiplier harvests the power from the magnetic field interacting withthe inductor. The output of the voltage multiplier is connected to astorage circuit, which, in one embodiment, is a capacitor. The output ofthe storage circuit is connected to a voltage regulating circuit. In oneembodiment, the voltage regulating circuit are series connected lightemitting diodes (LEDs).

The power supply provides power to the processor and transmitter. Theprocessor has one or more inputs. The inputs are connected to switches,sensors, and instruments. The processor monitors the inputs and providesan output of an identifier and data that is provided to the transmitter,which transmits the identifier and data via a wireless signal. Theidentifier is a code that identifies the transmitter system. Whenmultiple transmitter systems are used, it is desirable for the receiverto distinguish between the transmitter systems. The data sent with theidentifier represents the parameters monitored by the processor inputs.The transmitted wireless signal is sensed by a receiver that isresponsive to the wireless signal.

In some cases multiple wireless transmitters are deployed. Each one ofthe wireless transmitters monitors a different set of parameters or adifferent machine. For example, parallel processes may each have arotating machine with a corresponding wireless transmitter. In oneembodiment, each one of the wireless transmitters transmits at adifferent frequency or channel or with a different type of modulation.In this way, multiple parameters are monitored. In another embodiment,each wireless transmitter has a unique identifier that is transmittedwith the monitored data. To avoid collisions the rate of transmissionvaries between the wireless transmitters, such as each transmitter usinga different clock rate or schedule of transmission.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The above-mentioned features will become more clearly understood fromthe following detailed description read together with the drawings inwhich:

FIG. 1 is a functional block diagram of one embodiment of a singlesensor burst transmitter system.

FIG. 2 is a schematic diagram of one embodiment of a single sensor bursttransmitter system.

FIG. 3 a is a diagram showing the trigger signal applied to thetransmitter unit over time.

FIG. 3 b is a diagram showing the Vcc voltage applied to the transmitterunit over time.

FIG. 3 c is a diagram showing the pulse signal sent to the antenna overtime.

FIG. 4 is a functional block diagram of one embodiment of a multi-sensortransmitter system.

FIG. 5 is a schematic diagram of one embodiment of a power supply.

FIG. 6 is a functional block diagram of one embodiment of a wirelesstachometer system.

FIG. 7 is a schematic diagram for one embodiment of a signalconditioner.

FIG. 8 is a schematic diagram for another embodiment of a signalconditioner.

DETAILED DESCRIPTION

Apparatus for a multi-sensor transmitter system 40 is disclosed. Themulti-sensor transmitter system 40 senses and transmits data for one ormore parameters while being powered by a machine or device that hasperiodic, cyclic, or reciprocating movement.

FIG. 1 illustrates a functional block diagram of one embodiment of asingle sensor burst transmitter system 10. The system 10 includes amagnet 102 and a burst transmitter 100. The magnet 102, in oneembodiment, is attached to a moving object such that the magnet 102periodically moves past the burst transmitter 100. The burst transmitter100 interacts with the magnet 102 and transmits a pulse 306 each timethe magnet 102 passes by the burst transmitter 100.

The burst transmitter 100 includes an inductor 104, a delay 106, and atransmitter 108 that is connected to an antenna 110. The magnetic field112 of the magnet 102 engages the inductor 104 when the magnet 102 movespast the inductor 104. The magnetic field 112 of the magnet 102interacts with the inductor 104 and induces a pulse 302 in the inductor104.

The magnet 102 is secured to a part of a machine that moves in at leastone direction 114 relative to the inductor 104 in the burst transmitter100. The magnet 102, through the magnetic field interaction with theburst transmitter 100, provides the energy that powers the bursttransmitter 100. Also, the magnet 102 triggers the burst transmitter 100to transmit the signal 306 when the magnet 102 is proximate the inductor104. Although the illustrated embodiment depicts the magnet 102 asmoving in direction 114, it is the relative motion between the magnet102 and the inductor 104 that is relevant. For example, in anotherembodiment, the burst transmitter 100 is attached to the movingcomponent and the magnet 102 is stationary.

The magnet 102 is dimensioned relative to the moving part of the machinesuch that the magnetic field 112 is substantially a point source thatengages the inductor 104 for a shorter duration than the duration whenthe magnetic field 112 does not engage the inductor 104. That is, theinteraction of the magnetic field 112 with the inductor 104 occursbriefly compared to the long dwell time with no interaction by themagnetic field 112. The interaction of the magnetic field 112 occursduring an interaction interval, which can be expressed in units of timeor angular displacement. The dwell interval refers to the time orangular displacement where the magnetic field 112 does not interact withthe inductor 104. For those embodiments where a magnet 102 is attachedto a moving component of a machine, the magnet 102 will be substantiallysmaller than the moving component in order to minimize the mass added tothe moving component and to minimize any unbalancing effect from theaddition of the magnet 102. Typically, the ratio of the interactioninterval to the dwell interval will be about 1:10 or less. For example,in one embodiment, the magnet 102 is cylindrical and less than ½ inch indiameter. The magnet 102 is attached to a rotating pulley that is sixinches in diameter. In this example the interaction interval isapproximately 10 degrees or less and the dwell interval is approximately350 degrees or more, which results in the ratio of the interactioninterval to the dwell interval of 10:350.

The magnet 102 is attached to a moving component that moves in acyclical or repetitive manner such that the magnet 102 repeatedly movesproximate the inductor 104 at an interval that corresponds to somevariable to be measured, such as revolutions per minute (RPM). Forexample, in one embodiment, the magnet 102 is attached to a shaft of apump or motor. The magnet 102 moves in direction 114 as the shaftrotates. The rate of interactions of a single magnet 102 on the shaftwith the inductor 104 provides data on the rotational speed of theshaft. One interaction between the magnet 102 and inductor 104corresponds to one revolution of the shaft.

For slower moving devices, multiple magnets 102 are spaced at regularintervals and an appropriate scaling factor is applied to the sensedrate of interactions to determine the rate of movement. For example, aplurality of magnets 102 are attached to a conveyor belt at regularintervals to measure the speed of the conveyor belt. Each time a magnet102 moves proximate the inductor 104 the burst transmitter 100 transmitsa pulse 306. Either the time difference between pulses 306 or the numberof pulses 306 per unit of time are used to determine the speed of theconveyor belt.

The inductor 104 is responsive to the magnetic field 112 of the magnet102. The leads of the inductor 104 are connected to the transmitter 108.The interaction of the magnetic field 112 of the magnet 102 with theinductor 104 causes the inductor 104 to generate a pulse 302 that setsthe trigger Tr of the transmitter 108.

The delay 106 is connected between the reference or ground Ref of thetransmitter 108 and the supply voltage Vcc connection of the transmitter108. The delay 106 adds a short time delay to the pulse 302 from theinductor 104.

The transmitter 108 is a device that transmits a wireless signal throughan antenna 110. In one embodiment, the transmitter unit 108 causes awireless radio frequency (RF) signal to be sent from the antenna 110.The transmitter unit 108 is both powered and triggered by the magneticfield 112 of the magnet 102 interacting with the inductor 104. Whenmultiple single sensor burst transmitter systems 10 are used withinrange of a single receiver, the transmitters 108 are configured tominimize or reduce interference. For example, in one embodiment, eachtransmitter 108 operates at a specific frequency or channel differentfrom other transmitters 108.

FIG. 2 illustrates a schematic diagram of one embodiment of a singlesensor burst transmitter system 10. The illustrated embodiment of thetransmitter system 10 includes a magnet 102 and a burst transmitter 100.The burst transmitter 100 includes an inductor 104, a delay circuit 106,a transmitter 108, and an antenna 110.

In one embodiment, the magnet 102 is secured to a moving part of amachine. The magnet 102 moves in a direction 114 relative to theinductor 104. Because the magnet 102 adds mass to the moving part, themagnet 102 in one embodiment is a rare earth magnet, which ensures thesize is minimized and the magnetic field generated is as strong aspossible relative to the size of the magnet 102. In another embodiment,the burst transmitter 100 is secured to the moving part of the machineand the magnet 102 is stationary.

The inductor 104 is a coil that is responsive to the magnetic field 112of the magnet 102. In various embodiments, the inductor 104 is an airwound coil or a cored inductor. The inductor 104 is oriented such thatthe magnetic field 112 passing through the inductor 104 generatessufficient power to drive the transmitter 108.

The delay 106 includes an RC circuit with a resistor 202 and capacitor204 connected in parallel. The RC circuit 106 is connected between thereference, common, or ground Ref of the transmitter 108 and the supplyvoltage Vcc connection of the transmitter 108. The delay circuit 106adds a short delay to the voltage generated by the inductor 104 andapplies that delayed signal 304 to the supply voltage Vcc connection ofthe transmitter unit 108. The values for the resistor 202 and thecapacitor 204 in the RC circuit 106 are selected such that the voltageacross the capacitor 204 falls below the minimum required Vcc voltage312 within the period 324 between trigger pulses 304. That is, the timeto drain the capacitor 204 is less than the period 324 being measured.

The transmitter 108 is a low power device with a fast response time thatis operable with the amount of power generated by the magnet 102 movingrelative to the inductor 104. The transmitter 108 has a trigger input Trthat causes the transmitter 108 to output a signal from the antennaoutput ANT to the antenna 110 when the trigger input Tr is at or above atrigger voltage 312. In various embodiments, the antenna 110 is anexternal or built-in antenna operating at the frequency of thetransmitter 108.

In one example, the transmitter 108 is an amplitude modulated (AM)hybrid transmitter unit, such as the Model AM-RT4-315 sold by RFSolutions. The transmitter unit 108 is a complete, self-contained RFtransmitter that supports a transmitted data rate up to about 4 kHz. Thetransmitter unit 108 requires a supply voltage (Vcc) of between 2 and 14volts dc with a typical supply current of 4 mA at 5 Vdc. The minimuminput level is 2 volts dc with a maximum equal to Vcc. The transmitterunit 108 operates at a fixed frequency of 315 MHz with a range up to 70meters. The transmitter unit 108 has four leads: supply voltage Vcc,reference or ground Ref, trigger input Tr, and output for an externalantenna Ant. The transmitter unit 108 has an equivalent circuitcapacitance of 1 nF between the trigger input Tr and the supply voltageVcc connections, and an equivalent circuit capacitance of 100 pF betweenthe ground Ref and the trigger input Tr connections and between theground Ref and the supply voltage Vcc connections.

In such an example, the supply voltage Vcc signal 304 is delayedapproximately 0.6 milliseconds relative to the signal 302 applied to thetrigger input Tr of the transmitter unit 108. Such a delay is sufficientto ensure that the transmitter unit 108 transmits a signal 306 as soonas the supply voltage Vcc signal 304 is at a level sufficient to powerthe transmitter unit 108. That is, with the trigger input Tr at avoltage at or above the required trigger voltage 312, the transmitter108 outputs a signal as soon as the Vcc voltage reaches the minimumrequired Vcc voltage 314. With the transmitter unit 108 in this example,the minimum trigger input Tr and the minimum supply voltage Vcc are thesame, which is 2 volts. In the tested embodiment, the magnet 102 andinductor 104 combination produce a spike of 2.8 volts, which issufficient to operate the transmitter unit 108.

FIG. 2 illustrates a simplified schematic of one embodiment of a singlesensor burst transmitter system 10. The simplified schematic does notillustrate various connections that may be required to accommodatespecific components selected, for example, the transmitter unit 108 mayrequire a crystal or other frequency selection circuitry. An antennatuning or matching circuit may also be needed depending upon thecomponents selected. Those skilled in the art will recognize the needfor such wiring and understand how to wire such a circuit, based on thecomponents ultimately selected for use.

FIG. 3 a illustrates a diagram showing the trigger signal 302 applied tothe transmitter unit 108 over time t. FIG. 3 b illustrates a diagramshowing the Vcc voltage 304 applied to the transmitter unit 108 overtime t. FIG. 3 c illustrates a diagram showing the output pulse signal306 sent to the antenna 110 over time t. The output pulse 306 is asignal at the frequency of the transmitter unit 306, which is muchgreater than the frequency of magnet 102—inductor 104 interactions. Theoutput pulse 306 is shown as a square wave because of the magnitude ofthe frequency difference. The diagrams also illustrate the periodicnature of the signals that correspond to the rate of interaction betweenthe magnet 102 and the inductor 104. In the illustrated embodiment, theperiod 324 between spikes or pulses 302, 304, 306 is regular.

The inductor 104 generates a voltage spike 302 from the interaction ofthe magnetic field 112 of the magnet 102 as it moves by the inductor104. The inductor 104 is connected between the reference or ground Refand the trigger input Tr of the transmitter 108 such that the voltage atthe trigger input Tr is positive relative to ground Ref. The triggerspike 302 has a maximum voltage that is equal to or greater than theminimum required trigger voltage 312 at the time 310 the output pulse306 begins. The minimum required trigger voltage 312 is the voltagelevel required by the trigger input Tr of the transmitter 108 to send asignal.

The delay circuit 106 is connected between the reference or ground Refand the supply voltage Vcc connections of the transmitter 108. The RCcircuit 106 adds a short delay to the voltage spike 302 from theinductor 104 such that the supply voltage 304 reaches a level 310sufficient to power the transmitter 108 after the trigger input Tr hasreached a sufficient level to trigger the transmitter 108 to send apulse 306. The minimum required Vcc level 314 is the voltage levelrequired by the transmitter 108 to be energized and operable.

The Vcc voltage 304 enables the transmitter 108 to operate when the Vccvoltage 304 reaches the minimum required Vcc voltage 314 at time 310. Afirst vertical line 310 shows the relationship between when the Vccvoltage 304 reaches the minimum required Vcc voltage 314 and the othersignals 302, 306.

Referring to FIG. 3 a, the trigger spike 302 has a voltage that is equalto or greater than the minimum required trigger voltage 312 at the time310 the Vcc voltage 304 reaches the minimum required Vcc voltage 314.Because these two conditions are met (trigger voltage 302 at or greaterthan minimum trigger voltage 312 and Vcc voltage 304 at or greater thanminimum required Vcc voltage 324), the transmitter unit 108 sends anoutput pulse 306 starting at time 310.

The second vertical line 320 shows the relationship between when thetrigger signal 302 falls below the minimum required trigger voltage 312and the other signals 304, 306. The output pulse 306 ends at the time320 when the trigger signal 302 falls below the minimum required triggervoltage 312 or the Vcc voltage 304 falls below the minimum required Vccvoltage 314, whichever occurs first. In the illustrated diagrams, theoutput pulse 306 stop time 320 occurs when the trigger signal 302 fallsbelow the minimum required trigger voltage 312. The time width of theVcc voltage signal 304 at the minimum required Vcc voltage 324, minusthe amount of time delay introduced by the RC circuit 106, determinesthe width of the output pulse 306. that is, the width of the pulse 306is the time between the pulse start time 310 and end time 320.

FIG. 4 illustrates a functional block diagram of one embodiment of amulti-sensor wireless transmitter system 40. The multi-sensor wirelesstransmitter system 40 includes a magnet 102 that interacts with amulti-sensor transmitter 400. The multi-sensor transmitter 400 includesan inductor 104 connected to a power supply 402 that is connected to aprocessor 404 and a transmitter 108. The inductor 104, when it interactswith the magnetic field 112 of the magnet 102, is a power source for thepower supply 402. The power supply 402 provides power to the processor404 and the transmitter 108. The processor 404 has a multitude of inputs406, for example, inputs from sensors such as switches and transducers.The transmitter 108 has an input from the processor 404 and an outputconnected to an antenna 110.

As with the single sensor burst transmitter system 10, the magnet 102moves repetitively relative to the inductor 104. In one embodiment, themagnet 102 is attached to a machine part that reciprocates or rotatessuch that the magnet 102 periodically moves past the inductor 104 indirection 114. The magnet 102 has a magnetic field 112 that periodicallyinteracts with the inductor 104 to produce a pulse 302 in the inductor104. In one embodiment, multiple magnets 102 are attached to the machinesuch that the inductor 104 senses the magnetic field 112 at a rategreater than once per cycle or revolution. In this way the multi-sensortransmitter 400 remains functional with machines that have a lowreciprocating rate or a low number of revolutions per second.

The magnet 102 is dimensioned relative to the moving part of the machinesuch that the magnetic field 112 is substantially a point source thatengages the inductor 104 for a shorter duration than the duration whenthe magnetic field 112 does not engage the inductor 104. That is, theinteraction of the magnetic field 112 with the inductor 104 occursbriefly compared to the long dwell time with no interaction by themagnetic field 112. The interaction of the magnetic field 112 occursduring an interaction interval, which can be expressed in units of timeor angular displacement. The dwell interval refers to the time orangular displacement where the magnetic field 112 does not interact withthe inductor 104. For those embodiments where a magnet 102 is attachedto a moving component of a machine, the magnet 102 will be substantiallysmaller than the moving component in order to minimize the mass added tothe moving component and to minimize any unbalancing effect from theaddition of the magnet 102. Typically, the ratio of the interactioninterval to the dwell interval will be about 1:10 or less. For example,in one embodiment, the magnet 102 is cylindrical and less than ½ inch indiameter. The magnet 102 is attached to a rotating pulley that is sixinches in diameter. In this example the interaction interval isapproximately 10 degrees or less and the dwell interval is approximately350 degrees or more, which results in the ratio of the interactioninterval to the dwell interval of 10:350.

The processor 404 includes one or more inputs 406. The processor 404outputs a signal to the transmitter 108 that includes an identifier anddata. The identifier uniquely identifies the multi-sensor transmitter400 for the embodiment where several transmitters 400 are usedconcurrently with overlapping range. In this way a receiver is able toidentify the transmitter 400 and its corresponding data. The datacorresponds to the inputs 406 to the processor 404.

As used herein, the processor 404 should be broadly construed to meanany computer or component thereof that executes software. The processor404 includes a memory medium that stores software, a processing unitthat executes the software, and input/output (I/O) units forcommunicating with external devices. Those skilled in the art willrecognize that the memory medium associated with the processor 404 canbe either internal or external to the processing unit of the processorwithout departing from the scope and spirit of the present invention.

In one embodiment the processor 404 is a general purpose computer, inanother embodiment, it is a specialized device for implementing thefunctions of the invention. Those skilled in the art will recognize thatthe processor 404 includes an input component, an output component, astorage component, and a processing component. The input componentreceives input from external devices, such as the switches, sensors, andinstruments that can be connected to the inputs 406. The outputcomponent sends output to external devices, such as the transmitter 108.The storage component stores data and program code. In one embodiment,the storage component includes random access memory. In anotherembodiment, the storage component includes non-volatile memory, such asfloppy disks, hard disks, and writeable optical disks. The processingcomponent executes the instructions included in the software androutines.

When multiple multi-sensor transmitter systems 40 are used within rangeof a single receiver, the transmitters 108 are configured to minimize orreduce interference. For example, in one embodiment, each transmitter108 operates at a specific frequency or channel different from othertransmitters 108. In another embodiment, the multiple transmitters 108operate on the same frequency and the received signals aredifferentiated by the identifier sent by the transmitter 400. Becausethe signal has a short duration compared to the time between transmittedsignals, collisions are rare. In case of a collision of signals from twotransmitters 400, the next set of transmitted signals should not collidebecause the difference in the rotational speed of the magnet 102 issufficiently different to cause the transmitters 400 to transmit atdifferent times, assuming the transmission rate is tied to therotational speed of the magnet 102.

FIG. 5 illustrates a simplified schematic diagram of one embodiment of apower supply 402. The power supply 402 includes an energy harvester, orvoltage multiplier, 522, a storage circuit 524, and a voltage regulatingcircuit 526.

The magnet 102 moves periodically in a direction 114 that causes themagnet's flux 112 to induce a current in the inductor 104. The strengthof the magnetic flux 112 and the speed of the magnet 102 as it movespast the inductor 104 influence the magnitude and shape of the inducedcurrent signal. In various embodiments, the voltage across the inductor104 due to the induced current is selected by using a transformer or byadjusting the configuration of the inductor 104. In one embodiment, theinductor 104 has a length parallel to the magnet direction 114 that issufficient to produce the desired power from the interaction of theinductor 104 with the magnetic field 112 of the magnet 102.

The inductor 104 is a coil that is positioned near where the magnet 102moves. The leads of the inductor 104 are connected to the power supply402, which has an energy harvester 522, a storage circuit 524, and avoltage regulating circuit 526. In the illustrated embodiment, theenergy harvester 522 in the power supply 402 is a voltage multiplier.The voltage multiplier circuit 522 increases the voltage across theinductor 104 to a level suitable for use by the processor 404 and thetransmitter 108. The voltage multiplier circuit 522 includes a networkof capacitors 502, 506 and diodes 504 that has an output voltage 516,512 that is greater than the input voltage from the inductor 104. Thevoltage multiplier circuit 522 charges the capacitor 508 in the storagecircuit 524.

The storage unit 524 stores the energy from the inductor 104 at theoutput voltage 516, 512 of the voltage multiplier circuit 522. In theillustrated embodiment the storage unit 524 is a capacitor 508. Thecapacitor 508 has a voltage rating sufficient to accommodate the maximumvoltage from the voltage multiplier circuit 522. The capacitor 508 hassufficient capacitance to store the energy from the periodicinteractions of the magnet 102 with the inductor 104, considering thepower needs of the processor 404 and the transmitter 108.

The capacitance of the capacitor 508 affects the power storagecapability and the start up time before such capacity is available. Acapacitor 508 with high capacitance, for example, 0.33F, requiresseveral minutes from a cold start before being fully charged by theinteraction of the magnetic field 112 with the inductor 104. Oncecharged, the capacitor 508 is able to provide power for substantialperiods and/or power levels. A capacitor 508 with lower capacitance, forexample, 0.022F, is smaller in size, quicker to provide power after acold start, and provides power for shorter periods and/or at lower powerlevels.

The voltage regulating circuit 526 in the illustrated embodimentincludes a series of light emitting diodes (LEDs) 410. The LEDs 410,across the storage capacitor 508, serve to regulate the voltage outputof the power supply 402. Red LEDs have a forward voltage of between 1.6and 2.0 volts, depending upon the doping of the LED. For example, anoutput voltage of approximately 5 volts can be obtained with three LEDsbetween the ground 516 and the second output 512. An output voltage ofapproximately 3.2 volts can be obtained with two LEDs between the ground516 and the first output 514. Until the output capacitor 508 is charged,the output voltages 512, 514 will be less than the voltage drop acrossthe LEDs 510. The forward current through the LEDs 510 is limitedbecause the current from the inductor 104 and the voltage multipliercircuit is limited. Another embodiment of the voltage regulating circuit526 uses a Zener diode to control the output voltage 512, 514. Invarious embodiments, one or both of the outputs 512, 514 are used, basedon the needs of the processor 404 and transmitter 108.

Upon first starting up, the power supply 402 has a zero output voltage.As the magnet 102 interacts with the inductor 104, the voltagemultiplier circuit 522 charges the capacitor 508 in the storage unit 524to the sum of the forward voltages of the diodes 510 in the voltageregulator circuit 526. The voltage regulator circuit 526 maintains arelatively constant voltage until current is drawn through the powersupply 402. The voltage output 512, 514 remains somewhat constant untilthe output current level increases to the level where the capacity ofthe inductor 104 and voltage multiplier circuit 522 to keep the storageunit 524 charged is exceeded. The output voltage 512, 514 then falls.With an increasing load, that is, with a decreasing load impedance, whenthe output current level reaches a level where the magnet-inductor 102,104 interaction cannot supply the full energy requirement, the outputvoltage 512, 514 drops, as does the current. The output voltage 512, 514recovers only when the load decreases, that is, when the load impedanceincreases.

FIG. 5 illustrates a simplified schematic of one embodiment of a powersupply 402. The simplified schematic does not illustrate variousconnections and components that may be required to accommodate specificcomponents selected and/or desired circuit specifications. For example,the number of capacitors 502, 506 and diodes 504 in the voltagemultiplier circuit 522 depend upon the desired output voltage and powerdesired at the output 512, 514. In another example, the size of thecapacitor 508 in the storage unit 524 will vary depending upon thedesired start time (larger capacitance requires a greater charging timeupon startup) and the power desired for the transmitter 108 (largercapacitance allows for greater energy storage).

FIG. 6 illustrates a functional block diagram of one embodiment of awireless tachometer system 60. The wireless tachometer system 60includes a tachometer receiver circuit 600 and a conventional tachometer608. The tachometer receiver circuit 600 is responsive to a wirelesssignal from a transmitter 108 that sends pulses corresponding to arotational speed of a device. In various embodiments, the transmitter108 is one in a single sensor burst transmitter system 10, amulti-sensor transmitter system 40, a wireless system such as describedin U.S. Pat. No. 8,035,498 (hereby incorporated by reference), oranother wireless system that monitors a rotating device.

The tachometer receiver circuit 600 includes an antenna 602, a receiver604, and a signal conditioner 606. The antenna 602 and receiver 604detect the pulses corresponding to the rotational speed of a devicedesired to be monitored. The signal conditioner 606 is a circuit thatconverts the output of the receiver 604 into a signal that is compatiblewith a conventional tachometer 608. The wireless tachometer 60 monitorsengine speed in a vehicle with a wireless connection between the sendingunit and the wireless tachometer 60.

Typically, vehicles operate with a voltage of 12 Vdc. Wireless receivers604 provide an analog output signal at half the supply voltage becausethe receiver output is an ac signal that, at most, fluctuatespeak-to-peak between −6 and +6 volts, which is a range of 12 volts butwith a maximum voltage of half of the operating voltage. The nominalmaximum output of 6 volts for the receiver 604 is reduced furtherbecause of the level of the wireless signal fluctuates under normalconditions and receivers 608 are not intended to be operated at maximumgain for long term use. Accordingly, the conventional receiver 604operating at a 12 volt rail voltage has an output substantially lessthan 6 volts. For example, a 10 db reduction from maximum, which is notnormally considered a substantial reduction, results in an output levelof 0.6 volts, which is insufficient to drive a conventional tachometer608.

Conventional tachometers 608 require an input signal of 12 Vdc pulsesbecause the conventional tachometer 608 is configured to be connecteddirectly to the vehicle's coil or a tach output on an electronicignition. The output of conventional receivers 604 are not compatiblewith the input of conventional tachometers 608. To correct the mismatchof voltage levels, a signal conditioner 606 matches the output of theconventional receiver 604 to the input of the conventional tachometer608. Without the signal conditioner 606, the conventional tachometer 608cannot provide a reliable indication with only the output of theconventional receiver 604.

In one embodiment, the wireless tachometer system 60 functions with awireless input corresponding to a signal with two pulses per revolutionand with the conventional automotive tachometer 608 configured with asetting corresponding to a 6 cylinder engine. The two pulses receivedfor the wireless input correspond to a wireless transmitter sensing twomagnets on the rotating member for one revolution. For thoseconventional automotive tachometers 608 that include a pulse perrevolution (PPR) setting, the tachometer PPR setting is adjusted tocorrespond to the number of magnets 102 used.

FIG. 7 illustrates a schematic diagram for one embodiment of a signalconditioner 606-A for a wireless tachometer system 60. In theillustrated embodiment, an operational amplifier (op amp) 702 conditionsthe output signal 708 from the receiver 604 into a signal that iscompatible with the tachometer 608. The capacitor 704 and variableresistor 706 are connected across the gain connections of the op amp 702to control the level of the output 710.

In one such embodiment, the op amp 702 is an LM386, the capacitor 704 is10 μF, and the resistor 706 is 10K ohms. In another embodiment, the opamp 702 is an LM4861 and the resistor 706 is not used. The input 708 tothe signal conditioner 606-A is the low voltage output of the receiver604. That is, the input 708 to the signal conditioner 606-A is at anominal maximum of 6 volts. The gain of the signal conditioner 606-A issuch that the output 710 is at a nominal 12 Vdc, which is sufficient totrigger the conventional automotive tachometer 608 reliably. In one suchembodiment, the operational amplifier functions as a comparator with thegain set to minimize overdriving the operational amplifier whileavoiding saturation.

FIG. 8 illustrates a schematic diagram for another embodiment of asignal conditioner 606-B. In the illustrated embodiment, a step uptransformer 802 is used to convert the input 708 to the output 710. Inone such embodiment, the transformer 802 is a step up transformer with aturns ratio of 3:1 or greater. In one such embodiment, the transformer802 has a turns ratio of at least 5:1.

The input 708 to the signal conditioner 606-B is the low voltage outputof the receiver 604, which is at a nominal maximum of 6 volts. The ratioof the transformer 802 is such that the output 710 is at a nominal 12Vdc, which is sufficient to trigger the conventional automotivetachometer 608 reliably.

The output of the conventional receiver 604 is an alternating current(ac) signal. The transformer 802 steps up the receiver output voltage toa level that ensures reliable operation of the conventional tachometer608. In one such embodiment, the gain of the receiver 604 is set oradjusted so that the output of the transformer 802 is at or near theoperating voltage of the vehicle. In another such embodiment, the turnsratio of the transformer 802 is selected such that the output of thetransformer 802 is at or near the operating voltage of the vehicleconsidering the output of the receiver 604. For installations where thetransmitted signal strength is fixed and with a receiver 604 having afixed gain, the transformer ratio is selected to provide an output thatis greater than the minimum voltage requirement of the tachometer 608and less than the saturation or maximum voltage of the tachometer 608.

FIGS. 7 and 8 illustrate a simplified schematics of the signalconditioners 606. The simplified schematics do not illustrate variousconnections that may be required to accommodate specific componentsselected.

The multi-sensor wireless transmitter system 40 includes variousfunctions. The function of generating power is implemented, in oneembodiment, by the inductor 104, which interacts with the magnet 102.

The function of providing power to the processor 404 and the transmitter108 is implemented, in one embodiment, by the inductor 104, whichinteracts with the magnet 102, with the inductor 104 connected to thepower supply 402.

The function of harvesting power is implemented, in one embodiment, bythe voltage multiplier 522 and storage circuit 524. The power generatedby the inductor 104 interacting with the magnet 102 is collected andstored in the storage circuit 524.

The function of regulating the voltage of the power supply 402 isimplemented, in one embodiment, by the voltage regulating circuit 526.In one such embodiment, the voltage regulating circuit 524 includes aseries of light emitting diodes (LEDs) 510. In another such embodiment,the voltage regulating circuit 524 includes one or more Zener diodes.

From the foregoing description, it will be recognized by those skilledin the art that a self-powered, multi-sensor wireless transmitter system40 has been provided. The wireless transmitter system 40 has a minimalparts count, requires no external wiring for supplying power andconnectivity, and has a low cost of installation and maintenance.

While the present invention has been illustrated by description ofseveral embodiments and while the illustrative embodiments have beendescribed in considerable detail, it is not the intention of theapplicant to restrict or in any way limit the scope of the appendedclaims to such detail. Additional advantages and modifications willreadily appear to those skilled in the art. The invention in its broaderaspects is therefore not limited to the specific details, representativeapparatus and methods, and illustrative examples shown and described.Accordingly, departures may be made from such details without departingfrom the spirit or scope of applicant's general inventive concept.

What is claimed is:
 1. An apparatus for a self-powered wirelesstransmitter associated with a component that has a periodic motion, saidapparatus comprising: a magnet having a magnetic field, said magnetconfigured to attach to the moving component; an inductor responsive tosaid magnetic field when there is relative motion between said magnetand said inductor; a power supply circuit electrically connected to saidinductor, said power supply circuit including a voltage multiplierconnected to a storage circuit, said storage circuit connected to avoltage regulating circuit; a processor electrically connected to saidpower supply, said processor having at least one input that isresponsive to a corresponding external condition, said processor havingan output based on said at least one input; and a transmitterelectrically connected to said power supply, said transmitter connectedto said output from said processor, said transmitter connected to anantenna, and said transmitter sending a wireless signal corresponding tosaid output of said processor.
 2. The apparatus of claim 1 wherein saidvoltage multiplier has an output voltage greater than a voltage inducedacross said inductor by said magnetic field.
 3. The apparatus of claim 1wherein said voltage regulator includes at least one diode.
 4. Theapparatus of claim 1 wherein said output of said processor includes anidentifier and data, said identifier being a code identifying saidtransmitter, said data representing said at least one input.
 5. Theapparatus of claim 1 wherein said magnetic field interacting with saidinductor is a sole source of power for said processor and saidtransmitter.
 6. The apparatus of claim 1 wherein said magnet isdimensioned and configured such that said magnetic field issubstantially a point source when compared to a dwell interval.
 7. Theapparatus of claim 1 wherein said magnet is dimensioned and configuredsuch that said magnetic field has a ratio of an interaction interval toa dwell interval of no more than 1:10, wherein said ratio is defined asa relationship between a first time when said magnetic fieldperiodically interacts with said inductor and a second time when saidmagnetic field does not interact with said inductor.
 8. An apparatus fora self-powered wireless transmitter associated with a component that hasa periodic motion, said apparatus comprising: a magnet having a magneticfield; an inductor responsive to said magnetic field when there isrelative motion between said magnet and said inductor; a power supplycircuit electrically connected to said inductor, said power supplycircuit including a voltage multiplier connected to a storage circuit,said voltage multiplier having an output voltage greater than a voltageinduced across said inductor by said magnetic field, said magnetic fieldinteracting with said inductor is a sole source of power for said powersupply; and a transmitter electrically connected to said power supply,said transmitter configured to send a wireless signal.
 9. The apparatusof claim 8 wherein said magnet is configured to attach to a component ofa machine where said component moves relative to said inductor.
 10. Theapparatus of claim 8 further including a processor having at least oneinput that is responsive to a corresponding external condition, saidprocessor having an output based on said at least one input, said outputconnected to said transmitter wherein said wireless signal correspondsto said output of said processor, and said processor electricallypowered from said power supply circuit.
 11. The apparatus of claim 10wherein said output of said processor includes data, and said datarepresenting said at least one input.
 12. The apparatus of claim 11wherein said output of said processor further includes an identifier,and said identifier being a code identifying said apparatus.
 13. Theapparatus of claim 8 wherein said magnet is dimensioned and configuredsuch that said magnetic field has an interaction interval that issubstantially less than a dwell interval.
 14. The apparatus of claim 8wherein said magnet is dimensioned and configured such that saidmagnetic field has a ratio of an interaction interval to a dwellinterval of no more than 1:10, wherein said ratio is defined as arelationship between a first time when said magnetic field periodicallyinteracts with said inductor and a second time when said magnetic fielddoes not interact with said inductor as the moving component movesrelative to said inductor.
 15. The apparatus of claim 8 wherein saidtransmitter is connected to an antenna that transmits said wirelesssignal.
 16. An apparatus powered from a machine with a component thathas a periodic motion, said apparatus comprising: a magnet configured toattach to the component, said magnet having a magnetic field; aninductor responsive to said magnetic field when there is relative motionbetween said magnet and said inductor; a voltage multiplier electricallyconnected to said inductor, said voltage multiplier having an outputvoltage greater than a voltage induced across said inductor by saidmagnetic field; and a storage circuit electrically connected to anoutput of said voltage multiplier.
 17. The apparatus of claim 16 furtherincluding a voltage regulating circuit electrically connected to saidstorage circuit.
 18. The apparatus of claim 16 further including atransmitter electrically connected to said storage circuit, saidtransmitter sending a wireless signal corresponding to at least oneparameter being monitored.
 19. The apparatus of claim 18 furtherincluding a processor electrically connected to said storage circuit,said processor having at least one input that is responsive to acorresponding one of said at least one parameter being monitored, saidprocessor having an output based on said at least one input, saidtransmitter connected to said output from said processor, and saidwireless signal corresponding to said output of said processor.
 20. Theapparatus of claim 19 wherein said output of said processor includes anidentifier and data, said identifier being a code identifying saidtransmitter, and said data representing said at least one input.